Exceptions to These Rules

Some low-level commands have interlocks with the slit shutter (noted in the following tables) or perform more complex actions.

1. Slit shutter control commands await completion and confirm it by outputting a message. In addition, the Slit_Shutter OPEN command warns if the camera shutter is closed.
2. The ECHELLE (= E) command not only drives in the requested echelle but also enables the correct one (via ECH_ENABLE) so that the appropriate echelle angles will be controlled by subsequent commands.
3. HART_POS (= HP) not only drives the Hartmann masks as requested but in UCLES mode also ensures that the UCLES flap is in the beam.
4. PERISCOPE and FOCAL_MODIFIER commands ( PERI and FM) expect IN or OUT parameters, and decide which periscope and focal modifier to use based on whether the central wavelength from the most recent CONFIGURE was less than or greater than 5500 Å. RED and BLUE are also acceptable parameters, and override the default values. The focal modifier commands also automatically adjust the slit width and length to maintain the same image dimensions at the detector.